THE GEOLOGY OF EGYPT. 403 



bedded limestones, which contain Ostrea larva, 0. serrata, 

 Gryphea vesicularis, etc., and are clearly of Senonian age. 



Further north, at the foot of Jebel Attaka, Vaillant (31) 

 long ago discovered a series of Cretaceous rocks. They 

 consist chiefly of limestones, generally dolomitic, and in 

 these he discovered two fossiliferous bands. The lower 

 contained Hippitrites cornu-vaccinum and //. organisans 

 and the upper included Ostrea larva, Janira sexangularis, 

 etc. The former is very probably Turonian and the latter 

 Senonian. Here, as elsewhere in Egypt, the Cretaceous is 

 succeeded conformably by the Eocene. 



Eocene and Oli ipQcene- -The Eocene is bv far the most 

 widely spread formation in Egypt. On the west side of the 

 Nile it forms the extensive plateau which reaches from the 

 oases of Upper Egypt northwards as far as Cairo and the 

 Great Petrified Forest. In the Arabian Desert it occupies 

 most of the space between the valley of the Nile and the 

 crystalline core of the Red Sea Mountains ; the eastern 

 boundary nearly coinciding with a line joining Suez and 

 Kena (23). 



The formation is divided by Zittel into three stages :— 



Upper Eocene stage. 

 Mokattam stage. 

 Libyan stage. 



The Libyan stage forms the southern part of the great 

 Eocene plateau and crowns the escarpment which over- 

 looks the Farafra and Kharga oases. Lithologically there 

 is no definite line between it and the Cretaceous below ; 

 but the fossils are very different. The Libyan beds con- 

 tain Operculina libyca and nummulites, which in this region 

 have never been found along with Cretaceous fossils. 



The older division of the Libyan stage is well seen in 

 the southern escarpment of the Eocene plateau, and also in 

 the valley of the Nile between Esna and Thebes. It con- 

 sists chiefly of calcareous rocks, the lowest beds being 

 sometimes marly or sandy. The most characteristic fossil 

 is Operculina libyca, which sometimes fills whole banks. 

 Various nummulites also occur, such as N. Ramondi, N. 



